cmd/govulncheck/internal/govulncheck: skip loading unnecessary data
cmd/govulncheck/internal/govulncheck: skip loading unnecessary data

packages.{NeedTypesSizes, NeedCompiledGoFiles, NeedFiles} are not needed
for govulncheck later steps.

Change-Id: I3b232babff8ae97013285e1e2fff09cae2fe99ff
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/428895
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
Run-TryBot: Zvonimir Pavlinovic <490af24f3def1258d2f7e9b10b20e341f6c68320@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/vuln,golang/vuln